1. Field of the Invention
The present invention relates to an X-ray CT imaging device and an X-ray imaging method for performing CT imaging by detecting, by an X-ray detector, an X-ray directed from an X-ray generator toward a subject located between the X-ray generator and the X-ray detector.
2. Description of the Prior Art
Conventionally, in the fields of medical care and the like, CT (computerized tomography) imaging is performed. According to the CT imaging, an X-ray beam is directed toward a subject to collect projection data, and the obtained projection data is re-constructed on a computer to generate a CT image (volume rendering image, etc.).
CT imaging is performed as follows. A subject is located between an X-ray generator and an X-ray detector. While the X-ray generator and the X-ray detector are revolved around the subject, a cone-like X-ray beam (X-ray cone beam) is directed toward the subject from the X-ray generator. The results of the X-ray detection (projection data) are collected by the X-ray detector, and three-dimensional data is re-constructed based on the collected X-ray detection results. A device usable for performing such CT imaging is disclosed in, for example, Patent Document 1.
According to Patent Document 1, the CT imaging device described therein operates as follows. During CT imaging, a pair of channel collimators are displaced in front of the X-ray generator such that a CT imaging area (field of view (FOV)), namely, an area irradiated with an X-ray (hereinafter, referred as the “X-ray radiation area”), becomes circular or elliptical. Thus, CT imaging can be performed only on an area of interest of a patient, who is a subject of the CT imaging.
However, there is a case where the area passed by an X-ray cone beam generated by the X-ray detector and revolving, namely, a flux of X-rays revolving during the CT imaging, encompasses a high sensitivity site of a biological body that is sensitive to X-rays such as, for example, submandibular gland, parotid gland, sublingual gland, thyroid gland, or lens of the eyeball. In such a case, especially when the patient has abnormality in such a high sensitivity site, the X-ray flux passing the high sensitivity site exerts a large influence. Therefore, care should be taken when the CT imaging is performed.